The present invention relates to an optical fiber cable containing at least one optical filamentary material having a glass or silica core and a lower index of refraction sheath.
Optical filamentary materials are well known in the art for transmission of light along a filament length by multiple internal reflections of light. Great care is taken to minimize light losses along the length of the filament or, in other words, internal reflections are made as total as possible so that light applied to one end of the optical filamentary material is efficiently transmitted to the opposite end of the material. The light transmitting portion or core of the optical filamentary material is surrounded by a sheath having a lower index of refraction which minimizes the escape or absorption of light along the length of the filament. This sheath is normally transparent since an opaque sheath tends to absorb light. Although this sheath can be made from glass or a polymeric material, it is conventionally made from the latter due to increased toughness properties.
Optical filamentary materials can be divided into two general classes dependent upon the type of optically transparent core material. A first class of core material is thermoplastic in nature while a second class is made from glass or silica. The first class is generally superior both in toughness and in ease of making connections while the second class is generally superior in light transmission.
One disadvantage with optical filamentary materials with a glass or silica core is a tendency for the core to break due to its brittleness. Encapsulation of the filaments within a cable containing reinforcement and a protective layer has only been partially successful in overcoming the brittle quality of the core. A need exists for an optical fiber cable which provides increased resistance to breakage of a brittle core material.